The present invention relates to medical devices and more specifically to techniques for acquiring uncontaminated electrical signals from the brain and body, without the use of pre-amplification electronics, especially while located within the harsh operating environment produced by a functional magnetic resonance imaging (fMRI) system.
Conventional EEG, EOG, ECG, EMG, and other physiological signals are typically recorded using individually placed electrodes that are fixed on the scalp and body with adhesives or by the use of a cap type system. Examples of these techniques are those developed by Sams et al (U.S. Pat. No. 4,085,739) or Gevins et al (U.S. Pat. Nos. 4,967,038 and 5,038,782). In these placement methods, the electrodes are attached to amplifiers used to acquire and record the related electrical and physiological activity. These amplifier systems require a very low impedance contact with the skin and are very susceptible to emissions from other electrical equipment, such as an MRI device. In such an environment, the input stage of a conventional EEG, ECG or EMG amplifier is susceptible to the very large induced electrical and magnetic fields generated by a magnetic resonance imager to the point where the amplifier cannot function properly. In addition, these amplifier systems are almost always powered from an AC Voltage source and, therefore, radiate electromagnetic interference (EMI), which causes contamination of the anatomical and functional data acquired by the fMRI system and compromises the integrity of these data.
A prior attempt to collect EEG signals within the fMRI environment, by Ives et al (U.S. Pat. No. 5,445,162) is based on a battery powered analog pre-amplifier system in which individual electrodes are glued to the scalp and the electrical activity is amplified within the bore of the imaging device. The signals are then converted to light energy by additional analog circuits placed nearby the patient. While still within the harsh fMRI environment, these signals are communicated along fiber-optic cables outside the shielded room, which protects the imaging equipment from unwanted interference, to a secondary amplifier system that is located outside the shielded room and attached to a PC for collecting and processing the data. However, this optically coupled pre-amplification system is expensive, bulky, and cumbersome to operate. In addition, due to size restrictions within the head coil (located inside the imager) and the inability to use digital circuits in the design, due to broadcast interference from internal clock circuits, the AC-coupled nature of this devices makes it susceptible to large artifacts caused by transient signals produced during normal operation of the imaging system.
The problems of the prior art, described above, are solved, in accordance with the present invention, by providing an EEG Electrode Positioning System using an elastic head cap (hereinafter Quik-Cap), to position electrodes on the head and face to acquire electrical signals and communicate them to external amplifier equipment. The Quik-Cap provides a stretchable elastic cap and chinstrap portion capable of comfortably fitting a wide range of head size and shape variability. The Quik-Cap provides a plurality of electrode holders designed to be filled with a conductive electrolyte. In addition, the Quik-Cap provides a wire harness assembly that can be configured with either carbon or metal lead wires and is capable of interfacing with any type of commercially available amplifier system.
Some specific features and objectives of the invention include the following.
The present invention provides a low cost system for rapidly applying large numbers of electrodes on the head and body that is capable of acquiring signals inside an fMRI system and communicating them outside the shielded environment without the use of any electronic amplification.
It is another objective of the present invention to use carbon lead wires attached to the electrodes positioned on the head and body to limit the susceptibility of the system to contamination from an MRI system and to communicate signals outside a shielded fMRI environment to amplifiers attached to a PC for collecting and processing electrophysiological and other physiologically correlated data.
Another object of the present invention to use metal electrodes composed of Tin, Gold, Silver-Chlorided Silver, or a combination or amalgam of Silver-Chloride powders, each carried in soft rubber electrode mounts and connected to carbon lead wires to limit the susceptibility of the system to physiological and electronically induced contamination.
It is a still further object of the present invention to use carbon, carbonized plastic, or conductive plastic electrodes in connection with carbon lead wires to further limit the susceptibility of the system to physiological and electronically induced contamination.
It is a still further object of the present invention to use needle electrodes, implantible depth electrodes, or cortical surface electrodes in connection with carbon lead wires to further limit the susceptibility of the system to physiological and electronically induced contamination while recording signals directly from the brain or spinal chord.
It is a still further object of the present invention that a single electrode, or group of electrodes, may also be used to acquire signals from the eyes, heart or muscles, by providing a mechanism to position electrodes in the appropriate regions of the scalp, face, chest or body.
Still another object of the present invention is to permit a single lead wire, or group of lead wires, to be used to connect to and communicate signals from external transducer devices used to measure signals related to oxygen uptake, respiration, heart rate, impedance, motion, acceleration, force or other such signals.
Yet another feature of the present invention is to provide separable elastic cap, chinstrap, and wire harness portions to position electrode holders and electrodes on the head, face and body to acquire EEG, EOG, EMG, ECG and other physiologically correlated signals from humans while inside a magnetic resonance imaging system.